1. Field of the Invention
The present invention relates to a signal line and a manufacturing method therefor, and, more specifically, relates to a signal line that is capable of being easily inflected and reduces unnecessary radiation, and a manufacturing method therefor.
2. Description of the Related Art
As a signal line of the related art, for example, a multilayer circuit substrate described in Japanese Unexamined Patent Application Publication No. 2004-311627 is known. FIG. 6 is a cross-section structure diagram of a multilayer circuit substrate 500 described in Japanese Unexamined Patent Application Publication No. 2004-311627.
The multilayer circuit substrate 500 is configured using an insulation base material 502 (502a to 502d), a ground conductor pattern 504 (504a, 504b), and a strip-shaped conductor pattern 506. The insulation base material 502 includes thermoplastic resin such as liquid crystalline polymer or the like. The ground conductor pattern 504a is provided on the back surface of the insulation base material 502a. The ground conductor pattern 504b is provided on the front surface of the insulation base material 502d. The strip-shaped conductor pattern 506 is provided on the front surface of the insulation base material 502c. In addition, the insulation base materials 502a to 502d are laminated so as to be arranged from an upper side in a lamination direction to a lower side therein in this order. Accordingly, the ground conductor patterns 504a and 504b and the strip-shaped conductor pattern 506 form a stripline structure.
In addition, in the multilayer circuit substrate 500, the ground conductor patterns 504a and 504b and the strip-shaped conductor pattern 506 have configurations described below so as to improve the adhesion of the ground conductor patterns 504a and 504b and the strip-shaped conductor pattern 506 to the insulation base material 502. Specifically, the surface roughnesses of main surfaces where the ground conductor patterns 504a and 504b and the strip-shaped conductor pattern 506 adhere tightly to the insulation base material 502 are larger than the surface roughnesses of main surfaces located on the opposite sides of the corresponding main surfaces. Namely, the surface roughness of the main surface on the upper side of the ground conductor pattern 504a is larger than the surface roughness of the main surface on the lower side of the ground conductor pattern 504a. The surface roughness of the main surface on the lower side of the ground conductor pattern 504b is larger than the surface roughness of the main surface on the upper side of the ground conductor pattern 504b. The surface roughness of the main surface on the lower side of the strip-shaped conductor pattern 506 is larger than the surface roughness of the main surface on the upper side of the strip-shaped conductor pattern 506. According to such a configuration as described above, since the ground conductor patterns 504a and 504b and the strip-shaped conductor pattern 506 are embedded in the insulation base material 502, the adhesion strength of the insulation base material 502 is improved.
However, the multilayer circuit substrate 500 has a problem that it is difficult to inflect and use the multilayer circuit substrate 500. More specifically, the multilayer circuit substrate 500 is inflected so that the strip-shaped conductor pattern 506 forms a U shape. In this case, there exist a first inflection state in which the ground conductor pattern 504a is located on an outer periphery side and the ground conductor pattern 504b is located on an inner periphery side and a second inflection state in which the ground conductor pattern 504a is located on an inner periphery side and the ground conductor pattern 504b is located on an outer periphery side.
Here, in the first inflection state, from among the insulation base materials 502a to 502d, the insulation base material 502a located on an outermost periphery side is subjected to the largest tensile stress. However, the ground conductor pattern 504a adheres tightly to the insulation base material 502a on the main surface on the upper side. Since being manufactured using metal foil, it is hard for the ground conductor pattern 504a to stretch compared with the insulation base material 502a. Therefore, it is hard for the insulation base material 502a to fully stretch. As a result, it is hard for the multilayer circuit substrate 500 to be fully inflected in the first inflection state.
On the other hand, in the second inflection state, from among the insulation base materials 502a to 502d, the insulation base material 502d located on an outermost periphery side is subjected to the largest tensile stress. However, the ground conductor pattern 504b adheres tightly to the insulation base material 502d on the main surface on the lower side. Since being manufactured using metal foil, it is hard for the ground conductor pattern 504b to stretch compared with the insulation base material 502d. Therefore, it is hard for the insulation base material 502d to fully stretch. As a result, it is hard for the multilayer circuit substrate 500 to be fully inflected in the second inflection state. As described above, it has been hard for the multilayer circuit substrate 500 to be inflected in any direction.